Warmer weather creates slide hazard

Alpine closed after fractures developed

After almost six months, the Dec. 5 snow crust is continuing to
cause problems in the alpine as Blackcomb ski patrollers took the unusual step
of closing all but two lifts this past weekend due to the risk of avalanche.

According to Tony Sittlinger, senior avalanche forecaster for
Blackcomb Ski Patrol, the patrollers started to close the Lakeside area of 7
th
Heaven on Tuesday, May 13 in response to avalanches that were spotted outside
of the ski area boundary and patrol tests in the ski area. The risks got
progressively worse, with patrol closing sections of the alpine before making
the decision to close the Glacier Express and 7
th
Heaven lifts, as
well as the Horstman T-Bar on Sunday, leaving just the Excellerator and Crystal
lifts open to the public.

Sittlinger says it might be possible to open the south runs on
7
th
Heaven this week with cooler weather and sub-zero temperatures
returning to the alpine, but the risk at press time is still high.

“We were already closing areas for avalanches on Tuesday (May
13), and as the temperature has risen and the warm weather persisted the
closures were more and more widespread,” he said. “Inside the Blackcomb ski
area there have already been four size-three avalanches, full depth avalanches
or close to it, and all of those were in areas we closed.

“It’s going to take some time to calm everything down. There’s
still quite a bit of momentum in the snowpack and avalanches in excess of three
metres at the deepest point, which is virtually full-depth.”

Sittlinger is also warning backcountry skiers to stay out of
the alpine for the time being.

“We were seeing full depth avalanches on compacted, inbounds
terrain that had moguls,” he said. “We were able to predict them, close the
areas, and avoid any problems in the ski area, but outside there is less
compaction, uncontrolled cornices, and the potential for more deep slab
activity.”

Cornice failures and snow falling off rocky areas onto slopes
below have been identified as causing avalanches outside the ski area
boundaries.

The Dec. 5 snow crust was formed during a period of rain in the
high alpine across southern B.C. The wet surface quickly froze and was covered
by snow. Although the snowpack consolidated over the next month and a half —
the last in-bounds activity related to the Dec. 5 weakness was on Jan. 15 — the
latest warming cycle has brought the crust into play again.

“The whole snowpack is always changing and moving depending on temperature,
crystal type, density, and other variables, and with the warm temperatures
we’ve seen snow turn to water… and the snowpack start to creep,” said
Sittlinger. “When you get more free water into the snowpack it starts to
accelerate, which led to a lot of the big events we were seeing. Any
significant trigger onto a gliding snowpack, on top of that week layer, had the
potential to trigger a larger slab avalanche.”

Just as it took five days for the avalanche risk to reach its
highest point, Sittlinger says it could take just as long for the cooler
temperatures to stabilize the snowpack.

“We’re monitoring it closely. It may seem that things developed
rapidly, but it took days to get to the point where things were at their worst
on Saturday night and Sunday morning. It will take days for things to settle
down.”